The present invention relates to bearing cooling for high speed turbomachinery
Aircraft environmental control systems incorporate an air cycle machine, also referred to as an air cycle cooling turbine, for use in cooling and dehumidifying air for supply to the aircraft cabin for occupant comfort. On aircraft powered by turbine engines, the air to be conditioned in the air cycle machine is typically compressed air bled from one or more of the compressor stages of the turbine engine. This bleed air is passed through the air cycle machine compressor wherein it is further compressed and then passed through a series of heat exchangers including a condensing heat exchanger to cool the compressed air sufficiently to dehumidify it. The compressed bleed air being supplied to the compressor of the air cycle machine is typically precooled by passing it through a precooling heat exchanger.
The expanded and precooled turbine exhaust air is expanded in a second turbine to further cool the expanded air to a desired temperature for supply to the cabin as conditioned cooling air. To be suitable for use in such an air conditioning system of an aircraft, an air cycle machine must have four wheels, i.e. two turbines, a compressor and a fan. To achieve optimal aerodynamic efficiency, there is a need to utilize more than two journal bearings to support a shaft that connects the four wheels. When a shaft is supported on more than two journal bearings it is desirable to introduce a flexible link in the shaft so that the shaft may be constructed with a bending critical speed that is lower than a normal rotational speed of the turbomachine. Such a turbomachine is described in US Patent Application Publication No. 20110135463 dated Jun. 9, 2011 which publication is incorporated herein by reference.
A turbomachine that is constructed with three journal bearings may be constructed with two thrust bearings. All of these journal and thrust bearings may require cooling during operation of the turbomachine. Typically such cooling is provided with gas flow from one of the turbines. The cooling gas flow may be directed to the bearings through a complex combination of external tubing and internal passageways.
As can be seen, there is a need for a four wheel air cycle machine design that allows for distribution of bearing cooling gas flow through a simplified internal gas passageway system.